Observing Centaur Rocket Boosters

by Jason Hatton , SeeSat subscriber

There had been a number of posts in April 1998 to SeeSat about observations of flashing Centaur rockets, so I decided to do some research and determine how many of these are potentially observable. I've observed several of these recently and they are IMHO some of the easiest objects to observe in the high eccentricity orbits.

Atlas Centaurs are relatively large upper stage rockets, most of which are initially in geostationary type transfer orbits (i.e., an apogee of 36000 km and a perigee of a few hundred kilometers). What is of interest to visual satellite observers is that many flash, and so, can easily be observed at ranges of 10,000 km or more in binoculars or small telescope, often flashing at magnitude +6 or brighter. For people lucky enough to see these objects at perigee (100-600 km), they can be very bright indeed (mag +1).

The original Atlas Centaur and Atlas I Centaur rockets are cylindrical 9m x 3m rockets with a bare metal surface (an insulating fiberglass covering is jettisoned before reaching orbit), with twin engines.

Atlas II Centaurs are 10m x 3m, covered with an orange PVC foam. If this is anything like the material covering shuttle external tanks, it may darken with exposure to sunlight and so could alter the flash pattern of the rocket. Additionally, the tank surface is often decorated with mission logos/art work which may also alter the reflective properties of the surface.

The Atlas IIIA Centaur (formerly IIAR), scheduled to launch in 1999, is similar to the Atlas II Centaur rocket, except only a single engine is mounted on the centerline of the booster.

The Atlas IIIB Centaur (formerly IIARC), scheduled for 2002, has a two engine stretched tank booster.

Centaurs have also been launched on Titan rockets. Those on Titan-IIE rockets are fairly similar to Atlas Centaurs, whilst those launched on Titan-IVs have a larger (5m) diameter. You can see a Titan IV Centaur leaving earth orbit on a planetary journey to Saturn here .

The possible image of a Titan IV Centaur venting fuel launched on May 9, 1998 at 01:38 UT from a classified US ORION signal intelligence mission (USA 139) to a geosynchronous orbit can be found here (171k) . Photo was taken by Charles Cornwell. Specifics are found in photo.

centaurG117K centaurG101k

Two views of a Centaur G (designed for shuttle launch), but very similar to Centaurs used in Titan IV launches. Photo by Jason Hatton taken at the Space & Rocket Center in Huntsvillve, Alabama (1993).

Jonathan's Space Report and the PPAS flash measurement database were used to draw up a list of potentially observable Atlas Centaurs. This list is given below.

There are elements for 50 plus Atlas Centaurs (and several Titan Centaurs) in the "alldat.tle" file obtained from Mike McCants' web site. Several of these are likely to decay in the next couple of years. If you are planning on observing Centaurs with low perigees, it's probably a good idea to get fresh elements since the orbital period can decrease quite rapidly.

Potentially observable Atlas Centaur Rockets (July 1999)

 
 
 Atlas Centaur's
_____________________________________________________________________________________________________________
Norad                   Common          Target                  Flash   Year            Decay in        Notes
ID      Intl. Desn.     Name (r)        Orbit   incl.   period  Period  Meas.   Accel?  2 years?        
_____________________________________________________________________________________________________________
694     1963-47A        None            GTO     30.4    104     44.9    1997    D       N       
698     1963-47D        Fragment                        0.5     1997    A?              
700     1963-47F        Fragment                        65.5    1997    D               
701     1963-47G        Fragment                        2.09    1995    D               
739     1963-47H        Fragment                                        No obs.                 
3598    1968-110B       OAO-A2          LEO     30.5    99.5    S       1993    D       N       
4069    1969-69B        ATS-5           GTO     17.2    703     8.885   1998    S       N       
4882    1971-06B        Intelsat-4-2    GTO     28.2    650     5.64    1998    D       N       
6779    1971-116B       Intelsat-4-3    GTO     28      650     9.36    1998    D       N
5816    1972-03B        Intelsat-4-4    GTO     28      650     1.531   1998    D       N
6058    1972-41B        Intelsat 4-5    GTO     27.5    650     25.391  1997    A/var?  N
6155    1972-65B        OAO-3(C)        LEO     35      98.6    S       1997    S       N
6797    1973-58B        Intelsat-4-7    GTO     28      650     3.19    1998    D?      N
545     1974-93B        Intelsat-4-8    GTO     26      650     lp      1998    ?       N
7902    1975-42B        Intelsat-4-1    GTO     26      650     ~200    1998    D       N
8331    1975-91B        Intelsat4A-1    GTO     21.6    651     7.97    1998    A/var?  N
8621    1976-10B        Intelsat4A-2    GTO     21.8    650     lp      1983    A       N
8840    1976-42B        Comstar-1 (1A)  GTO     21.2    650     4.917   1998    S/var?  N
9329    1976-73B        Comstar-2 (1B)  GTO     21.3    650     21.22   1999    D       N
10025   1977-41B        Intelsat4A-4    GTO     21.3    650     5.38    1998    D       N
10722   1978-02B        Intelsat4A-3    GTO     21.5    650     lp      1991    D?      N
12908   1978-16C        FLTSATCOM F1deb GTO     26.4    170     17.86   1998    A       
10779   1978-35B        Intelsat4A-6    GTO     21.8    650     4.495   1998    D       N
10976   1978-68B        Comstar-3 (1C)  GTO     21.4    650     4.915   1998    D       N
12069   1980-87B        FLTSATCOM F4    GTO     26.1    162     8.626   1998    D       ?       
12445   1980-98B        Intelsat-5-2    GTO     23.7    225     14.285  1998    D       ?       
12363   1981-18B        Comstar-4 (1D)  GTO     20.7    650     3.02    1998    D       N       
12497   1981-50B        Intelsat-5-1    GTO     23.6    210     10.87   1998    D       ?       Double Maxima
12778   1981-73B        FLTSATCOM F5    GTO                             1981    S/var?          
13007   1981-119B       Intelsat-5-3    GTO     23.6    210     6.02    1997    D       ?       
13087   1982-17B        Intelsat-5-4    GTO                     17.21   1983    D               
13599   1982-97B        Intelsat-5-5    GTO                     3.31    1990    D               
14081   1983-47B        Intelsat-5-6    GTO                     2.93    1983    1               
15874   1985-55B        Intelsat5A-11   GTO     23      530     9.046   1998    D       ?       
16102   1985-87B        Intelsat5A-12   GTO     23      465.6   3.89    1996    D       ?       
 
(b) Atlas I Centaurs
_____________________________________________________________________________________________________________
Norad                   Common          Target                  Flash   Year            Decay in        Notes
ID      Intl. Desn.     Name (r)        Orbit   incl.   period  Period  Meas.   Accel?  2 years?        
_____________________________________________________________________________________________________________
20713   1990-65B        CRRES           Ellip   17      575     lp      1999    1       ?       
21907   1992-13B        Galaxy 5        GTO     19.7    640     18.21   1998    D       N       
22564   1993-015B       UHF-F1          Sub     27.2    137.3   ~20     1998    Var     12/1999 
22788   1993-56B        UHF-F2          Sub     26.9    219     6.83    1997    Var             
23133   1994-35B        UHF-F3          Sub     26.9    250     23.9    1998    A?      ?       
23858   1996-27B        SAX             LEO     4       94.9            No obs          09/2000 
 
(c) Atlas II Centaurs (Atlas II, IIA, IIAS)
_____________________________________________________________________________________________________________
Norad                   Common          Target                  Flash   Year            Decay in        Notes
ID      Intl. Desn.     Name (r)        Orbit   incl.   period  Period  Meas.   Accel?  2 years?        
_____________________________________________________________________________________________________________                                                                                
21804   1991-83B        Eutelsat-II-F3  Super   17.5    753     40      1995    1       N               (a)
21990   1992-32B        Intelsat-K      GTO     26.3    434     70      1994    1       ?       
22010   1992-37B        DSCS-III-B10    GTO                             No obs                  
22916   1993-074B       DSCS-III        GTO                             No obs                  
23414   1994-79B        Orion Atlant.F1 Super   30.56   2880            No obs          N       
23468   1995-03B        EHF-F4          Sub     26.8    470.3   lp      1998    A?      ?       
23554   1995-19B        AMSC-1          Super   26.1    510     ~30     1998    1       ?       
23590   1995-27B        EHF-F5          Sub     26.9    450     25.4    1995    1       ?       
23629   1995-38B        DSCS-III-B5     GTO                             No obs                  
23658   1995-43B        JCSAT3          Super   22.8    1640            No obs          ?               (b)
23697   1995-57B        EHF-F6          Sub     26.7    470     lp      1998    D       ?       
23742   1995-69B        Galaxy 3R       Sub     26.7    470     2.93    1998    Var     ?       
23780   1996-06B        Palapa C1       Super   21.7    1916            No obs          ?               (b)
23840   1996-20B        Inmarsat-3-F1   GTO     21.5    640             No obs          N       
23968   1996-42B        UHF-F/O-F7      Sub     26.9    471             No obs          ?       
24675   1996-70B        Inmarsat-3-F3   GTO     22.2    650     23      1997            N       
24733   1997-07B        JCSAT-4         Super   23.4    349             No obs          ?               (b)
24881   1997-36B        Superbird C     Super   25.6    1664            No obs          ?               (b)
24937   1997-50B        GE-3            Super   18.7    790             No obs          N               
        1998-05B        Capricorn       Eccen                           No obs                  
25240   1998-014B       INTELSAT 806    GTO     22.6    282.9           No obs          09/2000 
25259   1998-016B       UHF-F8          Sub     27      388.5   110     1998    1       ?       
25372   1998-037B       INTELSAT 805    GTO     22.9    520.4           No obs          ?       
25502   1998-058B       UHF-F9          Sub     26.9    444.5           No obs          ?       
25631   1999-006B       JCSAT-6         Super   25.6    2122            No obs          ?       
25674   1999-018B       Eutelsat W3     Super   20.2    811             No obs          ?      
________________________________________________________________________________________________________________________________
Key:                                                                            
Target orbit        
         GTO = Geostationary Transfer Orbit         
         Sub = Subsynchronous Geostationary Transfer Orbit        
         Super = Supersynchronous Geostationary Transfer Orbit        
         Ellip = Elliptical orbit
incl. = orbital inclination                                     
Period = orbital period                                 
Flash period = measured flash period in seconds from PPAS 8 database                                                    
lp = long period                        
Year Meas. = year of most recent flash period measurement,                                                   
No obs. = no observations reported                         
2yr decay = SATEVO predicted date of decay in next two years                                               
N = decay unlikely in near future                                       
? = perigee less than 400km, so decay possible in next few years                                       
Decayed? = no elements in alldat.tle, so probably decayed in last 9 months                          
Notes:                                  
(a) = listed as "Ariane rocket"                                 
(b) = old elements, possibly decayed or "lost"                                  
Deb = Debris or fragment (or reclassification????)                                      
Flash measurement - accelerating?                                               
    A = accelerating                                       
    D = Decelerating                                        
    S = Stable, little or no change in period"                                      
    Var = variable flash period                                     
    1 = only one measurement                                                                        
* Original Intl. Desn. = 1971-116B                                      
** The Capricorn rocket is in an approx. 45 deg incl. high eccentricity orbit.                                      

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